Question 1085573
You know that,
{{{sin^2(theta)+cos^2(theta)=1}}}
{{{(-3/4)^2+cos^2(theta)=1}}}
{{{9/16+cos^2(theta)=1}}}
{{{cos^2(theta)=16/16-9/16}}}
{{{cos^2(theta)=7/16}}}
{{{cos(theta)=0 +- sqrt(7)/4}}}
Since you know {{{cos(theta)<0}}}, 
{{{cos(theta)=-sqrt(7)/4}}}
So,
{{{tan(theta)=sin(theta)/cos(theta)}}}
{{{tan(theta)=(-3/4)/(-sqrt(7)/4)}}}
{{{tan(theta)=3/sqrt(7)}}}
{{{tan(theta)=(3/7)sqrt(7)}}}